JPH02213384A - Thread-detecting device for sewing machine - Google Patents

Abstract

PURPOSE:To make it possible to quickly detect a state of a thread being used up or breaking without a mechanical load being applied to the thread even if lots of dust are produced in sewing operation, by providing a detecting electrode which makes an electric signal according to the spatial movement of a bobbin thread, and a timing signal-generating device which synchronizes with the vertical motion of a needle, and a deciding device which discriminates whether electric signal is beyond a criterion or not. CONSTITUTION:When a bobbin thread 67 or a needle thread 68 passes through inside a detecting electrode 36 in a sensor 33, an electric signal according to its movement is induced around the detecting electrode 36, and the induced electric signal is led to a gate circuit 61 after amplified in an amplifier 40 and a main amplifier 60. On the other hand, a timing signal-generating device 53 synchronizes with both the vertical motion of a needle 18 and the motion of a rotating hook 23. A timing signal of the time when a bobbin thread 67 only exists and its bobbin thread is horizontally moved, thereby, is outputted to the gate circuit 61 through a gate signal-forming circuit 58. A comparator 62 in a deciding device 54 outputs the signal of 'thread exists' when a level of the signal from the gate circuit 61 is beyond a criterion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thread detection device for a sewing machine that detects when a sewing thread runs out or breaks.

[Conventional technology]

Conventional thread detection devices include the following. A piezoelectric element is brought into mechanical contact with a thread passing through a needle hole in a needle plate. When a thread is present during sewing, the piezoelectric element generates an electrical signal as the thread slides against the piezoelectric element. On the other hand, when there is no thread, the above-mentioned sliding movement disappears, and the piezoelectric element no longer emits an electric signal. The presence or absence of thread can be determined by the presence or absence of these electrical signals. Such devices include, for example, those shown in tlsP, N14.429.651.

[Problem to be solved by the invention]

In the above device, because the thread slides against the piezoelectric element, the thread becomes fluffy or the surface of the thread is scratched and becomes easily broken.

In order to eliminate the above-mentioned problem, it is conceivable to place the charging element so that the above-mentioned thread crosses the path of its light, and to detect the presence or absence of the thread based on whether the thread blocks the light or not.

However, with this method, dust generated from cloth or thread during sewing operations often accumulates in the light path and blocks the light. , it will incorrectly detect that there is a thread even though there is no thread.

The present invention has been made in view of the above points, and its purpose is to quickly detect when a thread is missing or broken while sewing cloth. An object of the present invention is to provide a thread detection device. As a result of this detection, it is possible to prevent the occurrence of large sewing scratches on the fabric or to prompt the replenishment of thread.

Another object of the present invention is to provide a yarn detection device that can detect the presence or absence of yarn without applying mechanical stress to the yarn.

Another object of the present invention is to provide a thread detection device for a sewing machine that can accurately detect the presence or absence of thread even if there is a lot of dust generated from cloth or thread during sewing.

[Means to solve problems]

In order to achieve the above object, the present invention takes the measures as described in the claims above, and its effects are as follows.

[Effect]

A sensing electrode is provided in the thread path in the sewing machine. When cloth is sewn in a sewing machine, the lower thread or upper thread moves spatially relative to its sensing electrode, and such movement of the thread causes the sensing electrode to receive an electrical signal corresponding to the movement.

On the other hand, the timing signal generating means generates a timing signal synchronized with the vertical movement of the needle in the sewing machine. The determining means receives an electrical signal from the sensing electrode and a timing signal from the timing signal generating means. Then, the electrical signal at the time of receiving the timing signal is compared with the reference value, and a discrimination signal corresponding to the comparison result is output.

〔Example〕

The drawings showing the embodiments of the present application will be described below.

FIG. 1 shows the general configuration of a sewing machine. The bed 10 of the sewing machine has a needle plate 11 with a needle hole 12. A hook 13 is provided below the throat plate 11.

On the other hand, above the throat plate 11 is a head 16 attached to a machine frame 15 of the sewing machine. The head 16 is equipped with a needle bar 17 that is movable up and down, and a needle 18 is attached to the lower end of the needle bar 17. The head 16 also includes a thread take-up 19, thread guides 20, 21, and the like.

The pot 13 has a well-known structure, and its outline is shown in FIGS. 7-10. Pot 13 is outer pot 23
and an inner pot 24 provided inside the pot.

The outer hook 23 is attached to a known hook drive shaft 25 and is rotatable. It also has a sword tip 26 and feathers 27 around it. On the other hand, the inner pot 24 is prevented from rotating by a hook stopper 28. As is well known, a bobbin case 29 is provided within the inner hook 24, and a bobbin around which a bobbin thread is wound is housed within the bobbin case 29.

Note that 30 indicates a thread guide provided in the bobbin case 29.

Next, the thread cutting stop device provided in the sewing machine will be explained. A sensor 33 in the stopping device is attached to the underside of the needle w, 11 as shown in FIG. The details are shown in FIG. 4, and FIG. 2 shows a top view of the sensor 33, and FIG. 3 shows a bottom view of the sensor 33. The sensor 33 has an insulating substrate vi, 34, and the insulating substrate 34 has a through hole 3.
5 is formed. An annular sensing electrode 36 is provided around the through hole 35 . The electrode 36 consists of a copper foil attached to one side and the other side of the insulating substrate 34 so as to surround the through hole 35, and a tube connecting the copper foil and provided along the inner peripheral surface of the through hole 35. (their surfaces are solder-plated). In this embodiment, the detection electrode 36 is formed into a complete circular ring shape, but it may be rectangular or partially cut off to form a C shape. and a shield electrode 37.3 surrounding the sensing electrode 36 on the other side.
It is equipped with 8. These electrodes 37° 38 are connected to the substrate 3
It consists of copper foil pasted on one side and the other side of 4. A preamplifier 40 with high input impedance is provided on one side of the insulating substrate 34. The amplifier 40 is FE7
41 and a diode 42 for protection.

Output terminals 43 and 44 of the amplifier 40 are provided on one side of the substrate 34, and one end of a connecting wire, for example, a shielded wire 45, which is passed through the substrate 34 from the other side, is connected thereto.

The other end of the connection line 45 is connected to the main amplification section of the discrimination means, which will be described later.

As shown in FIG. 4, the sensor 33 configured as described above is attached to the metal needle plate 11 by, for example, adhesive means, with the through hole 35 overlapping the needle hole 12 and an insulating layer 46 interposed therebetween.
It sticks to. The above-mentioned fixing means may be snap-fastening or other known methods. Further, as the insulating layer 46, a thin insulating plate or insulating paint is used. Furthermore, the sensor 33 is connected to the throat plate 1.
For example, a concave portion may be formed on the lower surface of 1, and the concave portion may be embedded therein.

As shown in FIG. 5, the sensor 33e may include an annular insulator 47 inside the detection electrode 36e. This insulator 4
7 prevents the detection electrode 368 from being worn out by the thread. Furthermore, the fifth
In the sensor 33e shown in the figure, parts that are considered to have the same or equivalent configuration as those shown in FIG. 4 in terms of function are given the same reference numerals as in FIG. .

Next, FIG. 6 shows a block diagram of the structure of the thread cutting stop device. The device includes a thread detection device 51 for detecting thread breakage or thread consumption in the sewing machine, and a stop device 52 for stopping the operation of the sewing machine in response to a signal from the detection device 51. The device 51 includes the sensor 33, timing signal generating means 53, and determining means 54.

The timing signal generating means 53 is composed of a detected object such as a metal piece 56 attached to the main shaft 55 of the sewing machine, a proximity sensor 57 using capacitance or magnetism, and a gate signal forming circuit 58. In such a timing signal generating means 53, when the detected object 56 rotates due to rotation of the main shaft 55, a detection signal is emitted from the proximity sensor 57 every time the detected object 56 approaches the proximity sensor 57, and the gate signal forming circuit 5
8 outputs a pulsed gate signal as a timing signal.

The determining means 54 includes a main amplifier circuit 60, a gate circuit 61, and a comparison circuit 62. The signal from the sensor 33 is amplified by the main amplifier circuit 60 and given to the gate circuit 61.

The gate circuit 61 outputs the signal from the main amplifier circuit 60 only when there is a gate signal from the gate signal forming circuit 58. The output signal is compared with a preset reference value in a comparison circuit 62, and the comparison circuit 62 outputs a signal corresponding to the comparison result.
When the signal from 1 is above the reference value, a thread presence signal, for example, a signal of "0" is output, and when it is less than the reference value, a thread absence signal, for example, a signal of "1" is output.

The stop device 252 receives the no-thread signal from the comparison circuit 62 and stops the motor that drives the main shaft of the sewing machine. A display 63, such as a lamp or a buzzer, is connected to the stop device 52 to indicate that the stop operation has been performed.

A power supply circuit 64 supplies operating power to each of the above circuits.

The sewing of the cloth using the sewing machine described above is as follows.

A cloth 65 to be sewn is stretched out on a cloth driving frame 66. The fabric 65 is moved along the upper surface of the bed 10 by moving the frame 66 in a horizontal plane by a known frame drive device. 65 on the right may be moved manually. When the main shaft 55 of the sewing machine is rotated by the motor, the hook drive shaft 25 rotates in conjunction with it, and the outer hook 23 rotates. Further, the rotation of the main shaft 55 causes the needle bar 17 and the thread take-up 19 to move up and down. Due to these movements, the above cloth 65
The bobbin thread 67 supplied from the bobbin in the hook 13 and the needle 18
Sewing is performed in a well-known manner using an upper thread 68 fed through the needle thread 68. The relationship between the rotation angle of the main shaft 55 and the operations of the balance 19, needle 18, and outer hook 23 is, for example, as shown in a and b in FIG.
, c.

The operation of the thread cutting stop device when sewing is performed as described above is as follows. When both the upper thread 68 and the lower thread 67 are supplied normally and sewing is performed normally, the lower thread 67 and the upper thread 68 move through the detection electrode 36 in the sensor 33, and the lower thread 67 As the outer pot 23 rotates, it is also swung laterally by the blades 27, as shown in FIGS. 7.8 and 9.10.

That is, the lower thread 67 and the upper thread 68 are connected to the detection electrode 3 in the through hole 35.
Move spatially relative to 6.

The upper thread 68 and the lower thread 67 are generally slightly charged.

For example, it has a negative charge. When such upper thread 68 and lower thread 67 move within the detection electrode 36, an electrical signal corresponding to the movement is induced in the detection electrode 36.

The induced electrical signal is transmitted to the preamplifier circuit 40 and the main amplifier circuit 6.
The signal is amplified by 0 and reaches the GEGOTO circuit 61. The signal is shown, for example, in FIG. 11d.

On the other hand, the timing signal generating means 53 generates a gate signal forming circuit 58 in synchronization with the vertical movement of the needle 18 and the rotation of the outer hook 23.
A timing signal (gate signal) is output from the gate circuit 61 to the gate circuit 61 . The timing signal is output when the rotation angle of the main shaft 55 is between 58'' and 110°, as shown in e in FIG. This is the time when only the bobbin thread 67 exists in the electrode 36, and the bobbin thread is swung laterally by the vane 27 as described above.

Gate circuit 61 receives both of the above signals and outputs a signal shown at f in FIG. 11 to comparator circuit 62. The comparison circuit 62 compares the level of the signal from the gate circuit 61 during the period of the timing signal with a reference value v1, for example, +10 mV. In the case of the signal f in FIG. 11, the level of the signal from the gate circuit 61 exceeds the reference value, so the comparator circuit 62 outputs a signal of "0" indicating that thread is present. Therefore, the stop device 52 is not activated.

On the other hand, if the bobbin thread 67 breaks or wears out and cannot be supplied normally, the signal given from the main amplification circuit 60 to the gate circuit 61 becomes as shown in g in FIG. The signal applied from the gate circuit 61 to the comparison circuit 62 is as shown in h of FIG. As is clear from the figure, since this signal is lower than the reference value v1, the comparator circuit 62 outputs the signal of rlJ with no yarn to the stop device 52.
Output to. The stop device 52 receives the signal and stops the motor that drives the main shaft 55, thereby stopping the operation of the sewing machine.

Further, the display device 63 is in a display state.

The timing at which the timing signal generating means 53 outputs the timing signal is preferably determined at a time when the difference between the presence and absence of the bobbin thread 67 appears most clearly in the signal obtained from the detection electrode 36. Since it differs depending on the structure, it is best to find it experimentally.

Next, FIGS. 12 to 16 show an embodiment in which not only the presence or absence of the lower thread can be detected but also the presence or absence of the upper thread can be detected in parallel. In this example, as shown in FIG. 12, in addition to the lower thread timing signal generating means 53f and the determining means 54f, the upper thread timing signal generating means 70 and determining means 74 are provided. The timing signal generating means 70 for upper thread, like the one 53f for lower thread, includes a detected object 71, a proximity sensor 72, and a gate signal forming circuit 7.
Consists of 3. Further, the upper thread discrimination means 74 includes a gate circuit 75 and a comparison circuit 76, similarly to the lower thread discrimination means 54f.

Detection of the lower thread and upper thread in this embodiment is as follows. The upper thread timing signal generating means 70 outputs a timing signal while the rotation angle of the main shaft is between 00 and 450 as shown in FIG. 16b.

When the angle is 0°, the relationship between the sensor 33f, the lower thread 6'lf, and the upper thread 68f is as shown in FIG. 13, and when the angle is 45°, the relationship is as shown in FIG. 15. Figure 14 is the first
This is a state on the way from the state shown in FIG. 3 to the state shown in FIG. 15. In the process where the rotation angle of the main shaft changes from 0° to 45@,
As shown in Fig. 13, the upper thread 68f comes out of the inner hook 24f, and the
As shown in Figure 4, the loop 69 of the upper thread 68f becomes smaller,
As shown in Fig. 15, the upper thread 68f is connected to the through hole 35f of the sensor 33f.
Completely come out of it. In other words, the needle thread 68f moves most thickly within the through hole 35f of the sensor 33f during the above process.
.

When both the upper thread 68f and the lower thread 67f are being supplied normally, the main amplifier circuit 60f outputs the signal shown in a of FIG. 16. As a result, the gate circuits 61f and 75 are connected to the first
The signals shown in d and e in Figure 6 are output. Each comparator circuit 6
2f, 76 reference value V2. Since the voltage exceeds V3, the outputs of the comparator circuits 62f and 76 are both signals indicating that the thread is present.

When only the bobbin thread 67f is cut or consumed and its supply is stopped, the output signal of the main amplifier circuit 60f becomes as shown at f in FIG. 16. As a result, gate circuits 61f, 7
The output signals of 5 are as shown in g and h of FIG. 16, respectively. The value of the output signal of the gate circuit 61f is determined by the comparator circuit 62.
Since it is less than the reference value v2 of [, the comparison circuit 62f outputs a signal indicating that there is no bobbin thread. Stop device 52f receives the signal and stops the operation of the sewing machine.

When only the upper thread 68f is cut or exhausted and its supply stops, the output signal of the main amplifier circuit 60f becomes i in FIG.
will be shown. As a result, the gate circuit 51f,
The output signals of 75 are as shown in j and k of FIG. 16, respectively. The value of the output signal of the gate circuit 75 is determined by the comparator circuit 76.
Since the value is below the reference value v3, the comparison circuit 76 outputs a signal indicating that there is no upper thread. Stop device 52f receives the signal and stops the operation of the sewing machine.

In the above embodiment, parts that are considered to have the same or equivalent structure as those in the previous embodiment in terms of function are given the same reference numerals as those in the previous embodiment with an alpha bent f, and redundant explanations are omitted. (Also, in the following embodiments, the same concept is used, and the g for alpha vent is added to omit the redundant explanation.) Next, in FIGS. 17 to 20, the lower thread is An embodiment will be shown in which the presence or absence can be detected.

Referring to FIG. 17, a spool 80 containing 68 g of upper thread is attached to the machine frame 15g. The upper thread 68g is passed from this spool 80 to thread guides 82 and 83, thread tension device 84, and head 16, which are attached to a frame 81 that is integrated with the machine frame 15g.
They are fed through thread tension devices 86, 87, which are respectively provided on supports 85 attached to g.

The sensor 33g of the thread detection device is attached to the support 85, and the upper thread 68g, which is kept taut, passes through the thread tension devices 84 and 86. The situation is the first
This is shown in Figure 8. When sewing is performed, the tensioned needle thread 68g is connected to the sensing electrode 36 of the sensor 33g.
The above-mentioned sensor 33g, which moves only intermittently forward in the g and does not oscillate laterally, has insulating plates 91, 92 inside a shield case 90 consisting of a main body 90a and a lid 90b.
It is housed in an electrically insulated state.

Detection of the presence or absence of a bobbin thread during sewing of cloth is performed as follows. When the lower thread and upper thread 6Bg are being supplied normally, the main amplifier circuit 60g outputs a signal as shown in a in FIG. 20. While sewing cloth, 68g of needle thread weighs 19g on the balance.
Since it progresses intermittently along with the vertical movement of , the amplitude of the first output signal increases each time it progresses. The timing signal generating means 53g outputs a timing signal during a period in which the amplitude of the output signal increases, as shown in FIG. 20b. During that period, the rotation angle of the main shaft 55g is, for example, 40° to
This is while the angle is 90°. This has a unique value for different sewing machines. When the output signal of the main amplifier circuit 60g is as described above, the output signal of the gate circuit 61g becomes as shown in C of FIG. Since this signal exceeds the reference value V4 of the comparator circuit 62g, the comparator circuit 62g outputs a signal indicating that the bobbin thread is present.

If the bobbin thread 67g is cut or exhausted and its supply is no longer available, proper sewing will not be possible. Then, the needle thread 68g advances very little. That is, the needle thread 68g connected to the cloth 65g is only advanced by being pulled out as the cloth 65g moves laterally.

When the needle thread 65g is not moved laterally, the upper thread 68g stops advancing. In this case, the output signal of the main amplifier circuit 60g becomes a signal as shown in d of FIG.

As a result, the output signal of the gate circuit 61g becomes as shown in e of FIG. Since the level of this output signal is lower than the reference value v4 of the comparison circuit 62g, the comparison circuit 62g is
Outputs a signal indicating no thread.

As described above, detecting the presence or absence of the bobbin thread by using the needle thread 68g has the following advantages. When the bobbin thread is sent out from the hook, it is sewn onto the cloth through an extremely short supply path. On the other hand, upper thread 68
g has a long supply path from being unwound from the spool 80 to being sewn onto the cloth 65g; therefore, the sensor 33
'g has a high degree of freedom in the location, i.e. spool 80
It may be placed anywhere in the supply path of the upper thread 6Bg from the needle 18g to the needle 18g, preferably at a place where the supplied upper thread 6Bg is unlikely to run sideways, and is set within the range from the thread guide 82 to the thread guide 20g. Good.

In the thread detection device of the embodiment described above, even if the upper thread 68g is broken or worn out, the upper thread 68g is detected by the sensor 33g.
8g of movement is eliminated. Therefore, the output of the detection electrode 36g disappears, and the same operation as described above is performed, that is, it is also possible to detect cutting or wear of the upper thread.

Further, in the determination means 54g, the signal from the main amplifier circuit 60g is directly transmitted to the comparison circuit 6 without using the timing signal generation means 53g or the gate circuit 61g.
2g, and the level of the input signal is the above reference value v4.
The following may be determined by confirming that the condition has continued for a predetermined period of time (for example, the time required for one sewing operation of a sewing machine).

〔Effect of the invention〕

In the present invention, when a thread is present, an electrical signal is obtained at the sensing electrode by the spatial movement of the thread relative to the sensing electrode.

On the other hand, if there are no threads, such electrical signals cannot be obtained. Depending on the presence or absence of these electrical signals, it is determined whether the thread is present or not. Therefore, the presence or absence of the thread can be determined without contacting the thread.

That is, the presence or absence of the thread can be detected without imposing any mechanical burden on the thread for the purpose of detecting it.

In the present invention, when a thread is present, an electric signal is obtained at the sensing electrode by actively moving the thread relative to the sensing electrode. On the other hand, even if dust generated from cloth or thread adheres to the sensing electrode, the dust remains substantially stationary relative to the sensing electrode. Therefore, the detection electrode does not receive a signal due to the dust.Thus, the detection electrode can obtain a clear signal depending on the presence or absence of thread, and the presence or absence of thread can be accurately detected.

[Brief explanation of the drawing]

The drawings show an embodiment of the present application, in which Fig. 1 is a partially cutaway side view of the sewing machine, Fig. 2 is a plan view of the sensor, Fig. 3 is a bottom view of the sensor, and Fig. 4 shows the TV in Fig. 2. -fV line enlarged sectional view, Fig. 5 is a sectional view similar to Fig. 4 showing different examples of the sensor, Fig. 6 is a block diagram of the thread cutting stop device, and Fig. 7 shows the lower thread and A diagram showing the relationship with the pot,
Fig. 8 is a plan view of the hook in the state shown in Fig. 7, Fig. 9 is a diagram showing the relationship between the bobbin thread and the hook at a different point in time from Fig. 7, and Fig. 10 is a plan view of the hook in the state shown in Fig. 9. Plan, 11th
12 is a block diagram of a thread cutting stop device according to a second embodiment of the present invention; FIG.
．． Figures 14 and 15 are diagrams showing the relationship between the sensor and the upper thread at different times, Figure 16 is a diagram showing various signal waveforms in the second embodiment, and Figure 17 is a diagram showing the relationship between the sensor and the upper thread at different times. A partially cutaway side view of the sewing machine showing the third embodiment, FIG. 18 is a horizontal sectional view showing the state of insertion of the needle thread into the sensor of FIG. 17, and FIG. 19 is a thread cutting stop in the third embodiment. FIG. 20 is a block diagram of the device, and is a diagram showing various signal waveforms in the third embodiment. 11... Throat plate, 13... Hook, 18... Needle, 33...
- Sensor, 53... Timing signal generation means, 54.
...Discrimination means. Figure 13 Figure 14 Figure 15 Figure 16 Figure 19

Claims (1)

[Claims] A needle plate having a needle hole, a hook provided below the needle plate, a needle that can move up and down provided above the needle plate, and a needle for detecting the presence or absence of the bobbin thread supplied from the hook. In the sewing machine, the thread detection device includes a detection electrode that is provided around the needle hole in the needle plate and that generates an electric signal corresponding to the spatial movement of the bobbin thread relative to the sewing machine; A timing signal generating means configured to generate a timing signal in synchronization with the vertical movement of the needle, an electrical signal from the sensing electrode, and a timing signal from the timing signal generating means; 1. A thread detection device for a sewing machine, comprising: a determining means for outputting a determining signal corresponding to whether or not the electric signal exceeds a reference value.